The goal of the proposed studies is the determination of the synaptic circuitry responsible for the generation of directionally-selective ganglion cell receptive fields in the rabbit retina. The rabbit retina contains several morphological and functional classes of ganglion cell. One such class is the On-center directionally-selective (ON-DS) ganglion cell; this cell type gives a characteristic excitatory response to patterned light moving in a particular "preferred" direction, and is inhibited by the same stimulus moving in the opposite "null" direction. These cells, which project to nuclei of the accessory optic system (AOS), play an important role in the reflex stabilization of oculomotor control of eye movements. The directional selectivity of ON-DS ganglion cells is generated by the inhibitory action of GABAergic neurons, and is further modified by the actions of cholinergic neurons. The experiments proposed here are designed to answer the following three questions. 1)What is the precise synaptic circuitry through which these GABAergic and cholinergic neurons generate the receptive fields of ON-DS ganglion cells? This question will be answered through the specific visualization of each of the components of the DS synaptic circuit. First, DS ganglion cells will be identified by retrograde transport of tracers injected into accessory optic system nuclei, followed by direct injection of fluorescent dye under microscopic control: work of other investigators has shown that ON-DS ganglion cells project exclusively to the AOS. Second, the cholinergic and GABAergic innervation of these presumed ON-DS ganglion cells will be examined by serial section electron microscopy, using ultrastructural immunocytochemical methods for the localization of glutamate decarboxylase and choline acetyltransferase. 2) What are the morphological classes of GABAergic amacrine neuron in the rabbit retina, and which of these classes interact with the ON-DS ganglion cell to generate its receptive field? This question will be answered through the direct impalement and dye filling of individual amacrine cells, their classification according to morphological criteria, and their classification as GABA neurons by immunocytochemistry. 3) Do outer layers of the rabbit retina contain heretofore unrecognized GABAergic neuronal elements, such as horizontal cells, that may play a role in the generation of DS? Recent work in other species has demonstrated directional selectivity in horizontal and bipolar cells. This question will be answered through the use of a highly sensitive immunocytochemical method for the localization of glutamate decarboxylase and GABA, and by the in vitro localization of high affinity uptake sites for GABA in the outer retina.